These books are new means "look, do you see these books? Let me tell you something about them: they're new!"
These are new books means "hey look here! You know what these thingies are? Not toys, not phones, they're new books"
The meaning is similar but in the former case you already postulate a previous knowledge of the books' existence and just add a feature, whereas in the latter you actually mention them for the first time.
"quelli libri sono nuovi" those is a totally different word and the difference is important in differentiation of subjects.
To quote the late Eric Morecambe, I used the correct words, but not necessarily in the correct order. However, in this context the exact sequence is not, for us English users, as important as the meaning. "These are new books" is just as correct as "These books are new" which you insist is the only acceptable interpretation of the phrase "Questi libri sono nuovi"